Pure Data running with Qjackctl under Ubuntu 9.10 on a Thinkpad T40

I get consistent DIO Errors in Pd - "A/D/A Sync" every few seconds causing audio drop outs.

I've tried all sorts of combinations of frame/buffer rates etc. in Jack with no joy.

It seems that something in Pd doesn't like Jack but not sure what I need to tweak. Any ideas?

Many thanks in advance.

Hi cmpmj:
Have you installed a real-time kernel? That may solve your issue. You can do it using synaptic. Also, check if your user belongs to the audio group. If not, you can add it with the dedicated ubuntu program or by typing:

# adduser <username> audio

There are also a couple of tweaks to the /etc/security/limits.conf by adding at the bottom of the text file:

# gedit /etc/security/limits.conf

@audio - rtprio 99
@audio - memlock unlimited
@audio - nice -10

These modifications above give higher priority to the audio group processes. Be careful because this could affect other programs performance.

Then you can configure jack with qjackctl. The following values resulted in good performance in my machine:

Realtime = yes
No Memory Lock = yes
Soft Mode = yes
Force 16 bit = yes (if you want to work with that samplerate)
Driver MIDI = seq

Priority = 70
Frames Periods= 128 or 256.

I wish you success.

Sumidero

Thanks for al the info.

I'm using a distro built on Ubuntu 9.04. Which package within Synaptic is the correct one to install a real time kernel?

i think it's "linux-rt", version 2.6.31.11.13. there's also a script available in synaptic for high audio priority for rt kernels, called "rtirq-init".